There are two, general operating modes from which GPS-derived
positions can be obtained—absolute and relative (or differential) positioning.
Within each of these two modes, range measurements to the satellites can be
performed by tracking either the phase of the satellite’s carrier signal or PRN
codes that are modulated on the carrier signal. In addition, GPS positioning
can be performed with the receiver operating in a static or dynamic
(kinematic) environment. This variety of operational options results in a wide
range of accuracy levels that can be obtained from the NAVSTAR GPS.
Accuracies can range from 100 meters down to less than 1 centimeter.
Increasing the accuracy to less than 1 centimeter requires additional
observation time and can be achieved in real time. The selection of a
particular GPS operating and tracking mode (for example, absolute,
differential, code, carrier, static, kinematic, or combinations thereof) depends
on the user’s application. Topographic surveying typically requires differential
positioning using carrier-phase tracking. Absolute modes are rarely used for
geodetic surveying except when worldwide reference control is being
established.